1. Field of the Invention
The present invention relates to a technique for preventing or suppressing degradation of a recorded state of a writable optical disk in an optical disk drive device.
2. Description of the Related Art
For example, JP-A-2006-309921 discloses an evaluation method of an optical recording medium in which the evaluation of playback durability of the optical recording medium can be performed in a short time and with high precision. Specifically, an operation laser power for heating a recording layer up to a recording operation temperature is obtained; the temperature of the recording layer when a laser beam having a specified playback laser power is irradiated at data playback is obtained based on the ambient temperature at the data playback, the playback laser power and the operation laser power; a relation between the playback laser power at the data playback and a playback endurance frequency is obtained; and a relation between the temperature of the recording layer at the data playback and the playback endurance frequency is obtained from the relation between the playback laser power at the data playback and the playback endurance frequency. However, no consideration is made on measures to enable the playback while the durability is kept.
In order to play back information recorded on an optical disk, a laser beam having a playback power is irradiated to the optical disk. According to standards, the disk must withstand more than one million times laser irradiation than the playback power. Until now, no serious problem occurs in CDs and DVDs. However, when a laser of a shorter wavelength is used for a high capacity optical disk based on the Blu-ray standard or HD-DVD standard, there is a tendency that even if the amount of power output is small like the playback power as compared with the record power, the laser has the energy amount to disrupt coloring matter coupling. Thus, in a writable optical disk, the state of recorded medium becomes liable to degrade by repeated playback, and the problem of the playback durability becomes serious.
It is ideal that in combinations of all commercialized optical disk drives and optical disks themselves, sufficient playback durability is obtained, and playback degradation does not occur in any playback environment, or does not reach such a level that a problem occurs in a recording and playback system. However, actually, the lasers of the optical disk drives and the optical disks have individual variations at the time of production and due to change over lapsed time, and the change of outside environment such as temperature also has an influence. Therefore, according to the related art, it is difficult to ensure a sufficient margin.